Method of making heat exchangers



Sept. 12, 1967 j UELL R ET AL 3,340,588

METHOD OF MAKING HEAT EXCHANGERS 2 Sheets-Shee1 1 Original Filed Oct.19, 1960 INVENTORS IgUE LLER 8r 1967 H. E. MUELLER ET AL 3,340,588

METHOD OF MAKING HEAT EXCHANGERS Sept. 12

2 Sheets-Sheet :3

Original Filed Oct. 19, 1960 FIG. 7

& Wm SR I N ME r T ML mm J IMS v .a W H 2m R mr E HOW United StatesPatent 3,340,588 METHOD OF MAKING HEAT EXCHANGERS Heinz E. Mueller,Littleton, C0l0., and Dietrich E. Singelmann, Buifalo, N.Y., assignorsto the United States of America as represented by the Secretary of theAir Force Original application Oct. 19, 1960, Ser. No. 63,691. Dividedand this application Dec. 11, 1962, Ser. No. 243,981

3 Claims. (Cl. 29157.3)

This application is a division of our copending application Ser. No.63,691, filed on Oct. 19, 1960, now abandoned.

This invention relates to a method of manufacturing spiral heatexchangers and particularly to the fabrication, assembly, andmanufacture of unusually large spiral heat exchangers designed to carrya fluid coolant therethrough.

In the design and production of heat exchangers for operation at extremetemperature differences, their size is generally limited to the size ofthe brazing furnace available. This is so because the conventionalmethod of manufacturing spiral heat exchangers is to first assemble theunit, then wind it in spiral form, and finally braze the wound unit in abrazing furnace. To produce unusually large heat exchangers, the size ofthe brazing furnace would necessarily be prohibitive for practical andeflicient operation. The present invention overcomes this problem bydisclosing a method of producing spiral heat exchangers of any desiredsize using a brazing furnace of ordinary proportions. This isaccomplished by first assembling the elements of the heat exchanger inproper relative position and then feeding the assembled unit through abrazing furnace. After the brazing operation has been completed the unitis wound into its spiral form to any desired size. Thus, it can be seenthat by manufacturing spiral heat exchangers in the manner hereindescribed, their final dimensions are not limited by the size of thebrazing furnace.

Accordingly, it is an object of this invention to provide a method ofmanufacturing unusually large spiral heat exchanger utilizing a brazingfurnace of ordinary size.

Another object of the invention is to 'provide a heat exchanger which iscapable of being wound after it has been brazed.

Still another object of the invention is to provide a method of windinga spiral heat exchanger after brazing by inserting filler blocks inalternate recesses in the radiating member to prevent collapse of thefin members.

A still further object of the invention is to provide a method ofwinding a spiral heat exchanger with corrugated fins brazed on bothsides of a fluid carrying tube section. To prevent meshing action of thefins of adjacent spirals, a separating strip is included therebetween.

These and other objects, features and advantages, such as simplicity ofconstruction and efliciency of operation, will become more apparent fromthe following description taken in connection with the illustrativeembodiments depicted in the accompanying drawings wherein:

FIGURE 1 shows a thin walled conduit through which the fluid coolantpasses;

FIGURE 2 shows a thin gauge corrugated metallic radiating member forattachment to the surface of the conduit shown in FIGURE 1;

FIGURE 3 shows a brazing furnace adapted to handle any length ofassembled fluid conducting and corrugated radiating members being fedthrough in a continuous brazing operation;

FIGURE 4 shows a section of brazed heat exchanger with filler blocksinserted in alternate recesses between the corrugations of the radiatingmembers to prevent col 3,349,588 Patented Sept. 12, 1967 lapse anddeformation of the fins during the winding operation;

FIGURE 5 shows an embodiment of the invention wherein only a singlecorrugated radiating member is attached to the surface of the conduit;

FIGURE 6 shows the heat exchanger of FIGURE 5 wound into a spiral shape;

FIGURE 7 shows another embodiment of the invention wherein a corrugatedradiating member is attached to both sides of the conduit; and

FIGURE 8 shows the conduit of FIGURE 7 wound into a spiral shape andincludes a spacer strip between adjacent corrugated fin layers.

Referring now to the drawings wherein like reference characters refer tolike elements in the various Views, in FIGURE 1 there is shown a thinwalled conduit 13 having an inner opening 15 for conducting a fluid heatexchanging medium therethrough. The conduit 13 is preferably fabricatedfrom a dense material such as copper, monel, or stainless steel and maybe polygonal, circular, or some combination thereof in cross-sectionalconfiguration.

Attached to the outer surface of said conduit 13 is a radiating member17 shown in FIGURE 2 which includes a plurality of corrugations 19 madeup of a series of recesses 21. The member 17 may be fabricated from athin metallic sheet which is crimped or corrugated into the desiredshape. The corrugations are rectangular in cross-section but may betriangular, hemispherical, or any other desirable shape.

In FIGURE 3 there is shown an assembled view of the conduit 13 andradiating members 17 passing through a brazing furnace 23, which has afront opening 25 therein. A platform 27 is provided upon which theassembled heat exchanger may be guided through the furnace 23. A rearopening (not shown) is also included in the furnace to allow the brazedportion of the assembled heat exchanger to pass therethrough similar toa conveyor belt arrangement. It will be noted that the brazing furnace23 is of relatively small size compared to that which would be requiredif the heat exchanger were spirally wound before brazing. The assembledheat exchanger may be of any desired length.

After the heat exchanger has passed through the brazing furnace 23thereby permanently attaching the radiating member 17 to the conduit 15,the assembly is ready to be spirally wound. In order to prevent bucklingor bending of the thin metallic fins of the radiating member 17 duringthe winding procedure, it is desirable to place the filler blocks 29 inevery other recess between the corrugations. These blocks (shown in FIG.4) may be made of wood, plastic or some low-temperature melting alloyand are to be removed after Winding.

In FIGURE 5 a simpler form of heat exchanger is shown having fins 17 onone side only of the conduit 13. When this assembly is spirally wound aunit of the type shown in FIGURE 6 results. This single radiating membertype of heat exchanger is most useful where a smaller size unit isrequired. Since the conduit 13 ordinarily ca-rries fluid underrelatively high pressures only a smaller size assembly of this typewould have strengthenough to withstand the internal forces acting on theconduit walls.

For the larger diameter heat exchangers, it is most desirable to mountradiating members on both the upper and lower surfaces of the conduit13. The radiating fins thus attached serve as reinforcements againstbulging out of the flat conduit by the force of the inner pressure. InFIGURES 7 and 8, there is shown the double radiating member type ofspiral heat exchangers. When this latter type assembly is wound it isnecessary to introduce a separating strip 31 in order to avoid a meshingaction of the adjacent radiating members 17 after the filler blocks 29are removed.

It should be understood that the drawings show only a single example ofradiating member fin shapes. Circular arc corrugations or pointedtriangular corrugations as Well as other shapes may be used in place ofthe rectangular embodiment shown. Also, a series of separate pipes maybe attached to the central fiuid conduit in a transverse direction inplace of the continuous fin producing strip. The pipe arrangement wouldoperate to cool the air as it passed through the individual openings.

One of the uses of the heat exchanger described herein is for coolingthe intake air which is rammed into the forward section of a jet engine.At extremely high speeds the intake air reaches temperatures which wouldbe detrimental to eflicient ope-ration of the engine. It is thereforenecessary to lower the ram temperature before the air reaches thecombustion chamber. This can be accomplished by means of the heatexchanger herein described by positioning within the engine air inletthe spirally Wound unit in such a manner that the incoming air wouldnecessarily pass over the radiating member and fluid conduit. Liquidhydrogen, which is used as a fuel in certain high altitudes, highvelocity flights, may be used as the coolant fluid. Because of the verylow temperature of the liquid hydrogen and the high temperature of theram air, a great deal of thermal expansion and contraction takes place.To allow the heat exchanger to follow these thermal movements, the coilis mounted so as to be free to wind and unwind to some extent. Incertain instances it may be desirable to tack-weld one spiral coilwinding to the next at selected spots in order to limit movements withinthe heat exchanger. In cases where larger pressure drops through the airpassages of the heat exchanger are expected, a cross frame behind theheat exchanger face can be arranged for load carrying purposes.

Although only certain embodiments of our invention have been describedherein, it will be apparent to those skilled in the art that variouschanges may be made in the construction and relative size of theelements without departing from the true spirit and scope of theinvention.

Having thus described our invention, what we claim as new and desire tosecure by Letters Patent of the United States is:

1. The method of fabricating a spiral heat exchanger having a meansprovided for conducting a fluid coolant therethrough comprising thesteps of positioning a corrugated radiating member in contact with theouter surface of a laterally elongated fluid conducting tubular member,brazing :said positioned members by passage through a heated furnaceusing a continuous brazing process, inserting filler blocks into therecesses in the corrugations of said radiating member, attaching aseparating strip to the outermost extremities of the corrugations onsaid radiating member, winding said brazed heat exchanger and attachedseparating strip into spiral form, said separating strip serving toprevent meshing action of adjacently disposed sections of saidcorrugating member, and removing said filler blocks from thecorrugations in said radiating member thereby allowing substantiallyfree passage of heat carrying gaseous fluid through the area betweenadjacent windings of the tubular member.

2. The method of fabricating a spiral heat exchanger comprising thesteps of flattening a circular tube to form a laterally elongatedtubular member, corrugating a thin metallic strip transversely to formradiating member having a plurality of recesses therein, positioningsaid corrugated strip on said laterally elongated tubular member suchthat the bottom walls of alternate recesses contact the outer wall ofsaid tubular member, brazing said positioned strip and tubular member bypassage through a heated furnace using a continuous brazing process,inserting filler blocks into alternate recesses in the corrugations ofsaid radiating member, winding said brazed heat exchanger into spiralform, and removing said filler blocks from the alternate recesses insaid corrugated radiating members thereby allowing substantially passageof heat carrying gaseous fluid through the area between adjacentwindings of the tubular member.

3. The method of fabricating a spiral heat exchanger having a meansprovided for conducting a fluid coolant therethrough comprising thesteps of positioning a corrugated radiating member having recessestherein on each side of a laterally elongated fluid conducting tubularmember, said corrugated members being positioned such that the bottomwalls of alternate recesses contact opposite outer walls of said tubularmember, permanently attaching said positioned radiating members to saidtubular member by passage through a heated furnace using a continuousbrazing process, inserting filler blocks into the recesses in alternaterecesses in the corrugations of said radiating members, attaching aseparating strip to the top wall of alternate recesses in one of saidbrazed radiating members, winding said brazed heat exchanger andattached separating strips into spaced convolute relationship such thatsaid separating strip serves to prevent meshing action of adjacentlydisposed corrugated mem bers, and removing said filler blocks from thealternate recesses in said radiating members thereby allowingsubstantially free passage of heat carrying gaseous fluid through thearea between adjacent windings of said sniral heat exchanger.

References Cited UNITED STATES PATENTS 2,693,026 11/1954 Simpelaar29-1573 3,007,680 11/1961 Harris 29-1573 X 3,021,804 2/1962 Simpelaar29157.3 X 3,071,187 1/1963 Fairbanks 29157.3 X

BENJAMIN A. BORCHELT, Primary Examiner.

SAMUEL FEINBERG, Examiner.

R. F. STAHL, Assistant Examiner.

1. THE METHOD OF FABRICATING A SPIRAL HEAT EXCHANGER HAVING A MEANSPROVIDED FOR CONDUCTING A FLUID COOLANT THERETHROUGH COMPRISING THESTEPS OF POSITIONING A CORRUGATED RADIATING MEMBER IN CONTACT WITH THEOUTER SURFACE OF A LATERALLY ELONGATED FLUID CONDUCTING TUBULAR MEMBER,BRAZING SAID POSITIONED MEMBERS BY PASSAGE THROUGH A HEATED FURNACEUSING A CONTINUOUS BRAZING PROCESS, INSERTING FILLER BLOCKS INTO THERECESSES IN THE CORRUGATIONS OF SAID RADIATING MEMBER, ATTACHING ASEPERATING STRIP TO THE OUTERMOST EXTREMITIES OF THE CORRUGATIONS ONSAID RADIATING MEMBER, WINDING SAID BRAZED HEAT EXCHANGER AND ATTACHEDSEPARATING STRIP INTO SPIRAL FORM, SAID SEPARATING STRIP SERVING TOPREVENT MESHING ACTION OF ADJACENTLY DISPOSED SECTIONS OF SAIDCORRUGATING MEMBER, AND REMOVING SAID FILLER BLOCKS FROM THECORRUGATIONS IN SAID RADIATING MEMBER THEREBY ALLOWING SUBSTANTIALLYFREE PASSAGE OF HEAT CARRYING GASEOUS FLUID THROUGH THE AREA BETWEENADJACENT WINDINGS OF THE TUBULAR MEMBER.